Article
Buttweld fittings change the direction or size of a pipeline, or branch it, and are joined to the pipe by a full-penetration butt weld. They are the standard choice for process piping above 2 inches, because the weld can be fully examined and the bore stays smooth.
The standards
ASME B16.9 sets the dimensions and tolerances of factory-made wrought buttweld fittings. The material is set by a separate standard:
- ASTM A234: carbon and alloy steel, with grades such as WPB (carbon steel, matching A106 Gr B pipe), WP11 and WP22 (alloy).
- ASTM A403: austenitic stainless steel, with grades such as WP304L and WP316L.
- ASTM A420: low-temperature carbon steel, grade WPL6.
- ASTM A815: duplex and ferritic stainless, such as WPS31803.
A fitting is therefore specified as, for example, "90° LR elbow, ASME B16.9, ASTM A234 WPB, 4 inch SCH 40".
Elbows
- Long radius (LR): centre-line radius 1.5 times the nominal size. The usual choice, with lower pressure drop.
- Short radius (SR): radius equal to the nominal size. Used where space is tight.
- Available in 90° and 45°, and as 180° return bends.
Tees
An equal tee has a branch the same size as the run. A reducing tee has a smaller branch. For a branch much smaller than the run, a weldolet or sockolet on the run pipe is often cheaper than a reducing tee.
Reducers
A concentric reducer keeps the centre line in line, and is used in vertical lines and where alignment is not critical. An eccentric reducer keeps one side flat. It is used on pump suctions, fitted flat side up, so that no air pocket forms at the pump inlet.
Other B16.9 fittings
Caps (to close a line permanently), stub ends (for lap joint flanges), crosses and return bends.
Wall thickness
A buttweld fitting must match the wall of the pipe it is welded to, so fittings are ordered by schedule, the same as pipe. A mismatch leaves a step inside the joint that has to be tapered, and a fitting thinner than the pipe weakens the line.
Seamless or welded fittings
Fittings are made from seamless pipe or from welded pipe and plate. The grade designation shows which: in ASTM A403, a suffix of S means seamless, W welded, and WX or WU indicate the extent of weld examination. Specify the construction if your project requires one.
What to put on the enquiry
The fitting type, angle and radius, the size (and both sizes for reducers and reducing tees), the schedule, the material standard and grade, and whether seamless construction is required.
See 90° buttweld elbows, equal tees and the full pipe fittings range.
Frequently asked questions
What does ASME B16.9 cover?
Dimensions, tolerances, ratings and marking of factory-made wrought buttweld fittings from NPS 1/2" to 48".
Are buttweld fittings rated by class?
No. Their pressure rating matches straight seamless pipe of the same material and wall thickness.
Which material specification is used for stainless buttweld fittings?
ASTM A403, with grades such as WP304L and WP316L.
Key takeaways
- B16.9 sets dimensions; ASTM A403 or A234 sets the material.
- Fitting wall thickness must match the pipe schedule.
- Specify type, size, schedule, grade, class and standard.
Need these products?
Sawariya Metal Industries supplies stainless steel pipes, flanges and buttweld pipe fittings from Mumbai to buyers in India and overseas. Send your size, grade, standard and quantity through our enquiry form and we will reply with a clear quotation and the test documents you need. You can also browse our stainless steel pipes, flanges and buttweld fittings.